The present invention pertains to medication delivery devices, and, in particular, to portable medication delivery devices such as injection pens.
Patients suffering from a variety of diseases, such as diabetes, frequently must inject themselves with medication, such as insulin solutions. To permit a person to conveniently and accurately self-administer proper doses of medicine, a variety of devices broadly known as injector pens or injection pens have been developed.
In order to permit a person to administer a proper dose, injection pens have been equipped with a wide variety of dosing and injecting mechanisms that enable a particular dosage to be conveniently selected and then dispensed. Generally, these pens are equipped with a cartridge including a plunger and containing a multi-dose quantity of liquid medication. A drive member is movable forward to advance the plunger in the cartridge in such a manner to dispense the contained medication from the opposite cartridge end, typically through a needle that penetrates a stopper at that opposite end. In reusable pens, after the pen has been utilized to exhaust the supply of medication within the cartridge, a user can remove and dispose of the spent cartridge. Then, to prepare for the next cartridge, the plunger-engaging drive member of the pen is reset to its initial position, either manually or automatically during attachment of a replacement cartridge, and the injection pen can then be used to the exhaustion of that next cartridge.
In order to allow the reset of the plunger-engaging drive member of reusable injection pens, a variety of assemblies have been utilized. One known assembly utilizes a nut fixed within the housing, such as by ultrasonic welding, which nut threadedly engages a drive screw that when rotated is extendable from the base of the injection pen to advance the plunger of a cartridge within a retainer mounted to the pen base. Rotation of the drive screw to screw it through the fixed nut to advance the plunger is effected by a toothed drive clutch, keyed to rotate with the screw, which engages a toothed drive member that rotates during operation of the injecting mechanism. The drive clutch, which is forced into torque transmitting relationship with the drive member when the cartridge retainer is mounted to the pen base, is spring biased away from the toothed drive member when the cartridge retainer is removed. While effective to advance the drive screw, and to allow that screw to be reset or pushed back into the pen base during the process of mounting the cartridge retainer, this assembly is not without its shortcomings. For example, due to the relatively large size of the drive clutch, a flywheel effect of the rotating clutch during screw resetting may cause the screw to retract so far that the initial priming of the pen may be inconvenient to perform.
Injection pens have been equipped with an assortment of mechanisms that generate an audible clicking noise during the injecting process. This clicking noise is intended to inform a user that the pen is operating to administer medication. One known pen uses an injection clicker mechanism which employs a series of radially extending leaf springs arranged around the periphery of a disk-shaped, radially projecting portion of a drive sleeve of the injecting mechanism. As the injecting mechanism of the pen is operated, the drive sleeve rotates, causing rotation of a clutch that has been axially moved during pen assembly so as to be engaged by teeth that axially extend in the distal direction from the drive sleeve radially projecting portion. As the clutch rotates, a drive screw that extends through the drive sleeve and to which the clutch is keyed is caused to rotate, and the drive screw advances axially as it screws through a nut within the pen housing to move a cartridge plunger and expel medicine from the pen. During the drive sleeve rotation, the radially extending leaf springs arranged around the drive sleeve radially projecting portion slip into and out of recesses in the pen housing located radially outward thereof, thereby producing audible clicking noises associated with injection. The leaf springs, when inserted in the housing recesses when drive sleeve rotation is halted, are designed to prevent counter-rotation of the drive sleeve which would allow undesirable back up of the drive screw. While useful, this injection clicker design is not without its shortcomings. For example, modifying the feel and sound of the injection clicks during the design of the pen may involve modifications to the mold cavities of the housing. Still further, the radially extending leaf springs may undesirably increase the overall girth of the injection pen.
In another injection pen disclosed in U.S. Pat. No. 5,688,251, an injection clicker is provided by a spring biased distal clutch with axially facing teeth which is coaxially arranged on and splined to a nut that engages an advanceable lead screw. The spring that pushes the distal clutch teeth against the housing bulkhead to create audible clicking during injection also pushes a proximal clutch against a driver to create audible feedback during dose dialing. While perhaps functional, this design is not without its shortcomings. For example, because the spring used within the injection audible feedback design is also used as part of the dialing audible feedback design, the injection audible feedback cannot be tuned or adjusted by modifying that spring without also affecting the dialing audible feedback, and potentially other features such as dialing torque.
Another limitation of reusable injection pens is that because different types of medicines, provided in separate cartridges, possibly may be utilized with the same reusable pen body, a user of the injection pen and those various cartridges needs to be vigilant to ensure the pen is used to administer the correct dosage of medicine. In order to assist a user in identifying medicine contained in a cartridge, a cartridge recognition system has previously been disclosed in U.S. Pat. No. 5,954,700. In that system, a medicine-filled cartridge includes an information providing source designed to provide information regarding the cartridge to the electronic delivery device, such as an injection pen for which it is adapted. While useful, the information provided does not necessarily result in the delivery device indicating to a user the actual dose of medicine being administered by the delivery device, and calculation errors on the part of the user are possible, resulting in incorrect doses.
Another limitation of some injection pens relates to the dose setting mechanism. One mechanism disclosed in U.S. Pat. No. 5,509,905 includes switches that are used in forming signals when the switches are actuated during rotation by a user of an operating head extending from the pen base. The signals are used in mathematically establishing the number of unit volumes set by the user. However, the use of cams to activate the switches results in the resistance to rotating the operating head noticeably varying during revolution of that operating head.
Another problem with some existing injection pens is that dosing and injecting operations of the pen are not intuitive to all users. In particular, with some pens, the user first must rotate a knob of the pen to set the medicine dose to be delivered as indicated by numbers on a marked dial fixedly connected with the knob, and then must apply an axial or plunging force which moves the knob axially to inject the medicine dose. Because for some pen designs the knob and dial will have axially translated away from the pen base while being rotated during dose setting, and further that knob and dial, when plunged during injecting, will also rotate back into the pen base so as to provide via its markings a continuous indication of the amount of medicine remaining to be delivered, a user may come to believe that rotating down the proximally extended knob will inject the medicine. However, such a belief is erroneous for at least one pen design, and therefore a user who operates under such an erroneous belief may not properly self-administer the desired medicine.
In a well known disposable injection pen design, a dose is similarly set by rotating out a knob, connected to a number-marked dial, such that the dial translates out while rotating. While the dial is rotated, a sequence of numbers helically arranged on the dial is visible through a viewing window to show the dose the pen is then set to deliver. In this design, application of a plunging force moves the knob and the dial axially and without rotation to inject the medicine dose. However, while useful, this design is not without its shortcomings. For one thing, during plunging, few if any of the dose-indicating numbers which have been passed in setting the pen are displayed, which may be a source of confusion for some users. Furthermore, after the pen is used for injecting, the dial has to be reset before it can be screwed outward to set the next dose for delivery. Resetting requires a rotation of the dial to a zero position, except for a limited number of dose quantities previously injected, followed by an axial shifting of the dial.
Thus, it would be desirable to provide a device or method that overcomes one or more of these and other shortcomings of the prior art.